In the hands of a skilled woodcarver, chisels and gouges are an excellent (and sometimes the only) hand tools that can cut virtually any contour on a workpiece. They are best used to cut specific shapes and details while working to layout lines, and for incising away sizeable chunks of waste material quickly. Often a mallet is used to drive the cutting edge into the wood. These tools are not as well suited to working areas of freeform surfaces to continuously blended finished contours, a task best performed by a tool that merely shaves or planes the surface, rather than cutting deeply into the wood under the skillful guidance, control, and physical effort of the woodcarver.
There are a great many designs and styles of woodworking hand planes and spokeshaves that have been developed over time, all to perform the same basic operation on a workpiece of wood or other workable material. That operation is to remove thin shavings of controlled thickness from a rough and/or uneven surface to render it smooth and even. When a perfectly flat surface is the objective, there are many designs to accomplish this task. From ancient wood-block planes to the most modem metal hand planes in current production, all have the same two features in common: a planar sole surface and a sharp-edged blade (traditionally called an “iron”) protruding slightly from the sole surface to shave material only from those areas of the workpiece that can come into physical contact with the sole.
In some cases, a convex surface or a concave surface must be made accurate in form and smooth in appearance. If the surface is cylindrical, a plane having a sole of complementary (matching) cylindrical curvature and a straight-edged iron can be used in the same manner as flat-soled planes are used on a planar surface. There are even some designs for planes with flexible soles that can be adjusted to match a desired curvature, and multi-piece soles whose elements can be positioned in relation to each other so they all will be in contact only with a certain cylindrical surface.
In general, a plane is adapted for work on a given flat, concave, or convex surface by machining its sole (the surface that contacts the workpiece) to have a complementary contour; i.e., flat, convex, or concave respectively. For compound-curved surfaces, the cutting edge of the blade can also be curved. Obviously, planes having flat or concave soles have limited utility on free-form three-dimensional surfaces because they can engage and cut only convex surfaces whose radius of curvature is less than that of the sole or the cutting edge. Work on any given three-dimensional free-form surface requires a plane having both a convex sole and a convex edge, each having a radius of curvature less than or equal to the smallest concave radius of curvature anywhere on the surface.
The cutting conditions on a three-dimensional compound-curved surface are quite different than on either planar or cylindrical surfaces. The sole of the plane is not in full contact with the work surface. Rather, contact occurs only in the vicinity of the mouth, through which the cutting edge of the iron protrudes. In order to maintain smooth cutting conditions, the plane must be guided over the work surface in such a way that the mouth is kept tangent to the work surface at all times. Sight and feel must be relied upon to selectively remove material only from those areas that are proud of the desired finished contour. The curvature of the sole has no influence upon the curvature of the surface of the workpiece unless the sole can come into substantially full contact with that surface.
A plane taking a full-width chip in hardwood, or even most softwood, requires a lot of force to push (or pull). For this reason, bench planes, with irons from 1.75 inches up to 2.63 inches in width, are designed to be held and used with two hands. Block planes are designed to be held and used with just one hand, and their irons are generally 1.38 inches wide, and not more than 1.63 inches wide, in order to limit the maximum force required to push the tool. They are often used to chamfer edges and corners, which limits the width of the chip and thereby minimizes the force required. However, when used to plane a flat surface, a block plane becomes much harder to push and control with just one hand, so the other hand is often needed to assist the gripping hand.
Aside from undesirably high force requirements, planes also have another characteristic that can cause great difficulty. Cutting “with the grain” is a term all woodworkers come to know and understand. This is especially important to the proper functioning of a plane, because cutting “against the grain” causes the iron to dig into the wood, lifting the fibers and splitting them apart ahead of the cutting edge rather than cutting them cleanly. Such a split will always extend below the line of cut, and the finished surface will have a defect (crater) in it that is called a “tear out”. In straight-grained woods, cuts can easily be made with the grain by good judgment gained from experience, and so-called “paring cuts” made across the grain at about a 45° angle to either side. However, there are woods having a curly grain pattern, such as Bird's Eye Maple and Tiger Maple, that cannot be planed in any direction without going against the grain in some portion of any cutting stroke. Here it is essential that the plane be able to cut freely and continuously without any tendency to “catch”, “dig-in”, or “stall in the cut” (common descriptive terms for typical interruptions of the cutting process). Whenever such an interruption occurs, it is likely to produce a tear-out in the surface. It should be noted that the lower the cutting force, the easier it is to control and maintain ideal cutting conditions at the cutting zone.